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Lost Racer physics data from RSC

Discussion in 'Racer' started by Tiberius, Jan 3, 2010.

  1. Hi all. I'm looking for some stuff which was posted at various times on RSC, some of the stuff posted for calculating car physics. Now RSC has gone it's all lost, I kept copies but have lost them. Here's what I'm looking for:

    - The formulas to calculate spring rates from weight/frequency - the formulas were posted by Mr Whippy as I remember.

    - The formulas to calculate damper rates, they were posted by Cosmo I think.

    - The car inertia.exe program, the one that we used to use to calculate the car body inertia.

    - The wheel inertia XML file that Miura posted.

    Also anything else that I've forgotten :tongue:

    Anyone got any of the above who could upload it?

    Cheers, Bruce.
  2. Thanks EoD, had lost both of those :)

    Does anyone remember the formulas for dampers and springrates? I thought I had the springrate calc written down somewhere but can't find it now. At the moment it's back to the old days of just changing numbers at random to get more/less understeer etc..

    Cheers, Bruce.
  3. Knut Omdal Tveito

    Knut Omdal Tveito
    Premium Member

    Hi tiberius

    I just made a quick spreadsheet to calculate the damping rates based on heave mode. I use spring rate as an input though...


    I did make a spreadsheet to calculate springrates but I have it on my other computer. I'll return from holiday on thursday and will upload it then:)
  4. For natural frequency vs mass and spring rate use...

    1/suspension rate + 1/tyre rate = 1/effective wheel rate

    NF = contact patch load * sqrt (eff wheel rate / ((0.5 pi sqrt (k/m) / g )

    NF = natural frequency
    pi = 3.14156...
    k = eff wheel rate
    m = mass
    g = 9.80655...

    You can re-arrange for whatever you want from that.

    As for damping, critical damping is...

    crit_damping = sqrt (4 * k * (contact patch load/g) )

    Shame RSC has lost so much info, lets hope they get some of it back!

    I have the inertia calc and the inertia PDF and all that kinda stuff saved, but not the threads themselves :(

  5. Thanks guys, I think they are both what I'm looking for (the formulas definitely are)..will take a look tomorrow :)
  6. Dave, sorry to sound dim here but what on earth is contact patch load? :)
  7. Basically the tyre load, or the load on that corner of the car in total.

    Just because it includes the tyre rate in the overall suspension/wheel rate (tyre + suspension), so you need to consider the tyres weight as well.

  8. Right, so it's basically just the sprung mass for that corner plus the unsprung (wheel/tyre etc) too? It's in kilos, right?

    Cheers :)
  9. Grrr, tried this formula every single way and can't get a usable figure out of it, I'm getting CPMs in the tens of thousands :-/

    Contact patch, is that in Newtons or kilos or something? It's in the same units as mass I presume? It should be giving me a CPM figure, shouldn't it, so somewhere in the ballpark or 60-120 or so?

    Whippy or someone, can you help with this? A working example that I can do on the calculator and check would be great, at least then I know what I should be getting and can work back from there :)
  10. Alexander Knoll

    Alexander Knoll

    hmm...the link is down... :( is there any chance to upload it here in the download section, please ;)
  11. Knut Omdal Tveito

    Knut Omdal Tveito
    Premium Member

    Yup. I'll dig it up or make a new one:)

    I would also recommend this site for some nice software:http://performancetrends.com/
    They have several software with free trial-periods.

    EDIT: As I understand it Racer now features moving suspension. Does that mean the dynamic roll-centre and camber is calculated as well? I downloaded the latest version and will try to get my car ingame on day in the future:)
  12. Hi Tiberius,

    Lemme see.

    I think I wrote it wrong, I was copying from my excel sheet.

    These are handy...

    critical damping = root(4mk)

    k = m * (nf/0.159).sq

    nf = root(k/m) * 0.159

    m = mass in kg
    k = spring/wheel rate in N/m
    nf = natural frequency

    There are lots of ways to choose critical damping and balance them off in bounce/rebound, and then you need to consider the shaft speed at which to apply these rates.

    The other formula are used to find good wheel, tyre and suspension rates, but again, it's all a rough guide.

    Suspension alignment and kinematics are really important too.

    I have some other really good bits of info that I have built up from over the years from all over the place, mainly on scraps of paper, so I'll try write them all up.
    We could do with a physics sticky thread that just has pure formula or analyses etc as reference material.

  13. Thanks Dave, it's working now..the figures I'm getting tie in nicely with what the converter on this page works out.

    Yeah, there's a lot of different ways to do things it seems, at the moment the damper curves are causing issues..of course the sport dampers on the Lambo are too powerful at low shaft speeds for a road car, even once you scale the curves down to a realistic level. Great handling car, great on the ring, but just *too* good for a realistic road car..even though the actual overall damper rates aren't that high. But putting linear rebound curves in makes the car *too* soft, it's just not right on turn-in and when the weight begins to shift around on hard cornering..it's just too soft. Been trying to find some shaft vs force data for normal road car dampers, but seems virtually everything is for race dampers.

    Yep, a dedicated physics thread would be great :)
  14. Dampers are hard.

    You can make what looks like a 5% change to peak damping rate at 1m/s shaft speed, but it might be nearly 20% change at certain shaft speeds (ie low speed 'handling' rates)

    You can alter behaviour a great deal with what on the curve editor look like small changes overall. Would be cool to have a zoom function really, kinda like a drag box to cover the area you want to see in more detail :)

    There was some road car damper data on RSC, for BMW E36 M3 and E30 M3 iirc... and lots of others. We just need to go find them all again, they are hiding out there :)

    Wanted to run a damper dyno on my own car too, just finding the time and money really.

  15. Knut Omdal Tveito

    Knut Omdal Tveito
    Premium Member

  16. I never picked up on this before, that car you designed looks ace..a long way from the screenshots I saw on RSC :). Looks like you did a lot of research into the design, have you worked out an actual suspension design yet or are the suspension/geometry settings still estimated for now? Would be great to be able to enter suspension geometry points and have the sim do all the calculations on the fly by itself, proper simulation for stuff like live axles are what Racer really lacks still. But I guess we'll never see that sort of change, would probably mean changing virtually everything about the way suspensions are set up in Racer at the moment? I suppose that the camber/toe change values go some way into simulating real suspension geometry once you've crunched the numbers? :)

    Glad you linked to the hemipanter site, I had that one bookmarked a long time ago but lost the links when I switched from my old computer. He mentions though that a lot of race cars are damped higher on bump than rebound. Stands to reason that bump/rebound ratios on a full tarmac race car will be different to an all-round road car, but bump rates being higher than rebound? Now I'm confused :)
  17. Knut Omdal Tveito

    Knut Omdal Tveito
    Premium Member

    Thanks. I don't remember what I posted on RSC, but I guess it was quite different! I started out making it for Racer, but there was more tutorials etc for GTLegends so I decided to go that route. However I'm keen to get it into Racer to see how far I can get with the Pacejka model.

    In GTL I do specify the pickup points. There is an option that adjust suspension rates due to motion ratio, however no one seems to use it. So GTL and Racer are similar in that respect. However GTL calculates the camber, toe, etc. Therefore bumpsteer etc is simulated. I seem to remember a "cambergain" variable in Racer though, is that correct?

    I tried to base my design on simulations and calculations as much as possible. I used CAD softwares like Solidworks and Inventor where I can get the exact inertia and mass of all components. They also got FEM modules to analyze deformations and stresses in the parts and can help save weight on most components.

    I found my simple excel file and will upload it now. EDIT: here it is Its very simple though, not sure how helpful it is since the equations has already been posted:)

    One question though. Do you guys have online races or do you mostly work on your cars? Would be fun to try it out:)
  18. Hi

    Needs "CarInertiaCalculator and inertiawheels" Those from the second post.

    Unfortunately links have expired. Please refresh.

    Thank you